Generally, it becomes necessary to suppress torsional rigidity while retaining a required torque and enlarge a torsional angle range of second stage in order to minimize booming noise during low speed running.
On the other hand, it is necessary to secure an extremely low rigidity and an extremely small hysteresis torque in order to minimize idling noise during idling.
In a conventional damper disc, however, it is impossible to effectively minimize both the foregoing idling noise at the time of idling and the booming noise at the time of low-speed running because space in the damper is too small to incorporate first and second stage torsion springs.
An object of this invention is to minimize the idling noise while securing low rigidity and low hysteresis torque by separating an output-side plate to both inside and outside at the time of idling, and to minimize the noise in low-speed running (booming noise) while retaining a wide torsional angle range by disposing torsion springs in series through float bodies at the time of low speed running.
Further objects are to minimize friction between the float body and a rectangular hole as far as possible in case when the torsion springs are disposed in series through the float bodies.
A still further object is to simplify manufacture of the damper disc by separating the output-side plate into a hub flange and an intermediate plate located at an outside thereof and by composing the intermediate plate with two plate members.